People pray at a makeshift memorial set up near the Inland Regional Center in San Bernardino.
Photograph: Jae C Hong/AP

Criminal profilers and behavioural analysts struggling to understand the impulses that lead to mass shootings like last week’s carnage in San Bernardino are racing to update their prediction and prevention models as the problem evolves in new, previously unthinkable directions.

A generation ago, mass shootings of this type were understood not as terrorism or a byproduct of out-of-control gun laws, but largely as a freak byproduct of mental or even physical illness. More recently, experts worried that saturation media coverage of random mass shootings was creating a copycat effect and emboldening perpetrators.

Now, the general understanding is that the media no longer serves to inspire would-be mass murderers, because perpetrators already know they can achieve instant notoriety with a well-enough executed plan. Rather, coverage of mass shootings acts a bit like an ever-expanding instruction manual, offering ideas on tactical approaches, types of weaponry, choice of targets, and so on.

The greater concern is the ready availability, via the internet, of extremist ideologies that speak directly to the perpetrators’ nihilistic desire to empower themselves through a cause larger than themselves. Experts, echoing the concern of policymakers from President Obama down, worry the ideologies themselves will spread and draw in more adherents as a result of the publicity attached to people carrying out mass slaughter in their name.

“What’s changed,” the forensic psychiatrist Park Dietz, one of America’s foremost criminal profilers, told the Guardian, “is that whereas in the past we had individuals who counted on the news media to make them famous and punish the world, now we have individuals inspired by organizations that use the news media as a weapon to disseminate propaganda and fear.” Indeed, Dietz said, the anxiety felt by the general population in learning about these events is one of their most insidious effects.

Politicians including President Obama have been quick to link the perpetrators of the San Bernardino shootings to Isis and see the problem in geopolitical terms, even without evidence that Isis itself did anything to further the plot. Professional profilers, by contrast, are more concerned about the psychological traits that can cause seemingly harmless individuals to erupt without warning in cold-blooded, meticulously planned acts of mass murder, whether they are inspired by Isis, white supremacy, or anything else.

The very fact that mass murders are now labelled either by psychological type or by ideology is already shocking to Mary Ellen O’Toole, who worked as one of the FBI’s top behavioral analysts and now leads the forensic science program at George Mason University.

“The quality of violence is so much more depraved than 30 years ago,” she said. “I honestly have to tell you, I don’t know that I expected to have a conversation all these many years later where we are distinguishing between different types of mass shootings. That’s what’s so concerning.”

The modern incarnation of what Dietz calls “pseudo-commando mass murder” and O’Toole calls a “mission-oriented maximum violence” is usually dated back to Charles Whitman, a former Marines sharpshooter who, in 1966, dragged an arsenal of rifles and handguns to a 28th-floor observation deck at the University of Texas in Austin and killed 11 people at random before being gunned down himself by a police officer. He had previously killed his mother, the wife who was about to divorce him, and three others who stood in his way up the tower.

At the time, Whitman was believed to have become unstable because of a series of professional and personal disappointments. When an autopsy revealed a small brain tumor, there was also speculation about his body chemistry being off.

The 1990s saw a spate of high school shootings, culminating in the 15 deaths at Columbine high school in 1999. Shortly after, Dietz noticed from the data that saturation media coverage of one mass shooting led almost invariably to another somewhere else in the United States within the next two weeks.

The Columbine killers, Eric Harris and Dylan Klebold, were themselves inspired by the 1995 Oklahoma City bombing, whose death toll of 168 they dreamed of topping. They hoped either Quentin Tarantino or Steven Spielberg would direct the film of their lives. Jared Laughner, who killed six people and injured others, including Representative Gabrielle Giffords, in Tucson in 2011, posted on his MySpace account: “I’ll see you on national TV!”

Some analysts began theorizing that the interrelationship between mass shootings and the media might create a snowball effect, especially as the internet sped up access to breaking news. But the number of maximum-impact mass shootings has not gone up significantly, even if their lethality has and even if the number of all mass shootings in the United States – including gang crimes and family killings – has reached more than one per day.

Instead, experts began seeing a new element creeping into the attacks: a political motivation, sometimes conjoined with a personal or workplace grievance. The first instance of that was the 2009 Fort Hood shooting, in which an army psychiatrist in touch with the al-Qaida operative Anwar al-Awlaki opened fire on his colleagues, killing 13 of them. Fort Hood also foreshadowed the debate that has erupted in the wake of San Bernardino over the label “terrorism” when applied to individuals using extremist ideology as a justification for violence they unleash largely or wholly by themselves. Several politicians, including President Obama called it terrorism, but the Pentagon and other US government agencies courted controversy by classifying it as workplace violence and prosecuting the perpetrator, Nidal Hasan, accordingly.

Professional profilers have differing feelings about the term terrorism, but their work tends to focus elsewhere because the label is not necessarily helpful in identifying at-risk individuals and either anticipating or preventing future attacks.

“Both mental illness and extremist ideology can put a human in the state of mind in which massive violence seems justified, and that can be any of a number of ideologies,” Dietz said. “What’s more significant to understand is how the person goes through life reaching this level of hostility and willingness to die, without anyone in their social environment blowing the whistle or stopping them.”

President Obama’s national address last Sunday might have urged American Muslims to confront the problem of extremism among their fellow believers “without excuse”, but these crimes are, more or less by definition, maddeningly difficult to spot because they tend to be committed by loners. “The more of a loner you are,” Dietz added, “the fewer people there are around to stop you or help you.”

Several commentators have noted how the San Bernardino shooters, Syed Rizwan Farook and Tashfeen Malik, were the first known married couple to have carried out a mass slaughter of this type. It is also highly unusual for new parents to commit multiple murders if the issue in question is not loss or harm to their baby. Dietz ascribed these circumstances to the power of the nihilist message the couple appear to have absorbed from Isis over the internet.

“The necessary ingredients for an attack of this kind are to be willing to die that day and an inclination to blame other people, either out of paranoia or a direct grievance,” Dietz said. “It turns out these are both fertile areas for jihadist propaganda, whose whole appeal is to blame the infidel and die for the glory of Allah.”

This article was amended on 10 December 2015 to correct Dr Park Dietz’s title from forensic psychologist to forensic psychiatrist.